$\dfrac{6}{8} - \dfrac{1}{5} = {?}$
$ = {\dfrac{6 \times 5}{8 \times 5}} - {\dfrac{1 \times 8}{5 \times 8}} $ $ = {\dfrac{30}{40}} - {\dfrac{8}{40}} $ $ = \dfrac{{30} - {8}}{40} $ $ = \dfrac{22}{40}$